According to a Microsoft press release, the new Dublin facility uses free cooling 95 per cent of the time, relying on nothing but the outside Irish air to keep its compute hardware from overheating.

"Air-handling units on the roof of the data center...draw outside air down into the facility to cool the server rooms, and then return hot air back out to the roof," reads a blog post from Arne Josefsberg, Microsoft's general manager of infrastructure services and global foundation services.

"Traditional data centers, on the other hand, cool server rooms with chillers, which consume a great deal of power and water. No chillers are used in the Dublin data center."

Microsoft has grasped the chiller-free holy grail in part because its server rooms can operate at temperatures as high as 95 degrees Fahrenheit (35 degrees Celsius). Most facilities keep their rooms between 68 and 72 degrees Fahrenheit, but Google and others have long advocated running at much higher temperatures to save the power costs that come with cooling. Earlier this year, the American Society for Heating, Refrigerating and Air-conditioning Engineers (ASHRAE) raised its recommended temps to between 77 degrees to 80.6 degrees.

But if its rooms rise above 95 degrees, Microsoft does have a back-up. "If it ever exceeds that temperature, or in the extremely rare event of external air quality issues such as a nearby fire, Direct eXpansion (DX) cooling will be used. DX is a simpler means of mechanical cooling that is normally used for residential, automotive, or light commercial applications."

Google, it would seem, does things a little differently. There is no mechanical cooling backup. The Mountain View Chocolate Factory has told Data Center Knowledge that when outside temperatures get too high at its Belgium facility, it offloads all tasks to other custom-built Google data centers, which now number about 36 worldwide.

Speaking at a mini-conference this summer, Google senior manager of engineering and architecture Vijay Gill seemed to indicate the company can respond to such temperature spikes automatically.

"You have to have integration with everything right from the chillers down all the way to the CPU," he said. "Sometimes, there's a temperature excursion, and you might want to do a quick load-shedding - a quick load-shedding to prevent a temperature excursion because, hey, you have a data center with no chillers. You want to move some load off. You want to cut some CPUs and some of the processes in RAM."

In typical Google fashion, he didn't provide specifics, but hinted the company could almost instantly move loads from data center to data center without human intervention.

"How do you manage the system and optimize it on a global level? That is the interesting part," Gill said. "What we’ve got here [with Google] is massive - like hundreds of thousands of variable linear programming problems that need to run in quasi-real-time. When the temperature starts to excurse in a data center, you don’t have the luxury to sitting around for a half an hour...You have on the order of seconds."

He would not say whether such a technology is in place today. When The Reg asked uber-Googler Matt Cutts about this mystery load-shifting technology, he said: "I don't believe we have published any papers regarding that." Which is as close as we're going to get to confirmation that the technology exists. If it does, we question whether it's actually been deployed in Belgium.

Microsoft's new facility - which it calls its first "mega data center" in Europe - carries a $500m price tag. It began operations on July 1, running such online Microsoft services as Bing, the Microsoft Business Productivity Online Suite, Windows Live, and the Windows Azure development and hosting platform.

The 303,000-square-foot data center can generate up to 5.4 megawatts of critical power, but Microsoft says it could potentially be expanded to generate 22.2 megawatts. Josefsberg says that by forsaking chillers, the facility will use less than 1 per cent of the water that traditional data centers use each year - and cut its Power Usage Effectiveness (PUE) rating approximately in half. ®